Modify a single plane mesh to match image based on alphas, create shape keys
If the animation will be planar (2D) I suggest you to subdivide the continents in a 2D software (Gimp, Krita, Photoshop), make a transparent PNG for each and import every continent as "Image as planes" (it's an addon), without caring the shape of the mesh; then you can set one location "jointed" and - some frames away - the location "drifted".

If it will be 3D, all PNG planes should be subdivided, shrinkwrapped to a sphere and moved with a rotation with pivot point centered in the center of the sphere.